1. Field of the Invention
The present invention relates to a narrowband microstrip type bandpass filter adapted to a home network, telematics, an intelligent traffic system, and a satellite Internet and, more specifically, to a microstrip type bandpass filter, in which a pattern can be simplified by optimizing the design and the manufacturing process to provide low-cost millimeter-wave parts, the manufacturing cost can be reduced by miniaturizing the parts, and the mass production can be readily realized.
2. Discussion of Related Art
Recently, a millimeter-wave application has been proposed in a field such as a home network, telematics, an intelligent traffic system and a satellite Internet. To succeed in these markets with the millimeter wave technology, one should reduce the cost and size of the parts considerably.
FIGS. 1A and 1B are pattern diagrams for illustrating a microstrip type bandpass filter according to a first example of the prior art, in which FIG. 1A is a pattern diagram for a bandpass filter having an attenuation pole at an upper side of the passband, and FIG. 1B is a pattern diagram for a bandpass filter having an attenuation pole at a lower side of the passband.
Referring to FIGS. 1A and 1B, the bandpass filter according to the first example of the prior art are formed with a cross coupling and an open loop resonator, which have a microstrip type asymmetric frequency characteristic, comprising an input terminal 10, an output terminal 11, an input resonator 12, an upper resonator 13, and an output resonator 14.
Here, an electric coupling 18 between the input terminal 10 and the input resonator 12, an electric coupling 15 between the input resonator 12 and the upper resonator 13, an electric coupling 16 between the upper resonator 13 and the output resonator 14, an electric coupling 19 between the output terminal 11 and the output resonator 14, and a magnetic coupling 8 between the input resonator 12 and the output resonator 14 are formed, respectively.
Further, as shown in FIG. 1A, since the input terminal 10 and the output terminal 11 contact with the input resonator 12 and the output resonator 14, an electric coupling 18 between the input terminal 10 and the input resonator 12 and an electric coupling 19 between the output terminal 11 and the output resonator 14 do not exist.
When a signal is input through the input terminal 10, the input signal is electrically coupled 18 between the input terminal 10 and the open loop input resonator 12, and the signal electrically coupled 18 is transferred again to the upper resonator 13 by the electric coupling 15 with the open loop upper resonator 13, and transferred to the open loop output resonator 14 through the electric coupling 16 between the open loop upper resonator 13 and the open loop output resonator 14. In addition, the transferred signal is transferred again to the output after selecting the characteristic band through the electric coupling 19 between the output terminal 11 and the open loop output resonator 14.
The coupling provided in FIG. 1A is largely composed of an electric coupling, and the coupling between the open loop input resonator 12 and the open loop output resonator 14 is an electric coupling. Therefore, the attenuation pole characteristic is formed at the upper side of the band, and the attenuation pole characteristic and the frequency are adjusted using a cross coupling.
In addition, the coupling provided in FIG. 1B is largely composed of an electric coupling, and the coupling between the open loop input resonator 12 and the open loop output resonator 14 is a magnetic coupling, so that the attenuation pole characteristic is formed at the lower side of the band.
However, although the open loop resonator is suitable for a wireless communication system adapted to a high selectivity channeling and low insertion loss, only one attenuation pole is formed and a design is limited based on the dielectric coefficient. [J. S. Hong, M. J. Lancater (1999.02), “Microstrip cross coupled trisection bandpass filters with asymmetric frequency characteristics”, IEE proc Microwave and antennas propagation, Vol 146. No 1, pp. 84-90].
FIGS. 2A and 2B are pattern diagrams for illustrating a microstrip type bandpass filter according to a second example of the prior art, in which FIG. 2A is a pattern diagram of a bandpass filter having an attenuation pole at the upper side of the passband, and FIG. 2B is a pattern diagram of a bandpass filter having an attenuation pole at the lower side of the passband.
Referring to FIGS. 2A and 2B, the bandpass filter according to the second example of the prior art is formed with a cross coupling and a triangular patch resonator, which have a microstrip type asymmetric frequency characteristic. Here, a filter using the triangular patch resonator has a small size and forms one attenuation pole at a high/low frequency of the passband by the electric coupling and the magnetic coupling.
In other words, the bandpass filter using the triangular patch resonator comprises an input terminal 20, an output terminal 21, an input resonator 22, an upper resonator 23, and an output resonator 24.
An electric coupling 28 between the input terminal 20 and the input resonator 22, an electric coupling 25 between the input resonator 22 and the upper resonator 23, an electric coupling 26 between the upper resonator 23 and the output resonator 24, an electric coupling 29 between the output terminal 21 and the output resonator 24, and a magnetic coupling 27 between the input resonator 22 and the output resonator 24 are formed, respectively.
Further, as shown in FIG. 2A, since the input terminal 20 and the output terminal 21 contact with the input resonator 22 and the output resonator 24, an electric coupling 28 between the input terminal 20 and the input resonator 22 and an electric coupling 29 between the output terminal 21 and the output resonator 24 do not exist.
When a signal is input through the input terminal 20, the input signal is electrically coupled 28 between the input terminal 20 and the triangular patch input resonator 22, and the signal electrically coupled 28 is transferred again to the triangular patch upper resonator 23 by the electric coupling 25, and transferred to the triangular patch output resonator 24 through the electric coupling 26 in the triangular patch upper resonator 23. In addition, the transferred signal is transferred again to the output after selecting the characteristic band through the electric coupling 29 between the output terminal 21 and the triangular patch output resonator 24.
The coupling provided in FIG. 2A is largely composed of an electric coupling, and the coupling between the triangular patch input resonator 22 and the triangular patch output resonator 24 is an electric coupling. Therefore, the attenuation pole characteristic is formed at the upper side of the band, and the attenuation pole characteristic and the frequency are adjusted using a cross coupling.
In addition, the coupling provided in FIG. 2B is largely composed of an electric coupling, and the coupling between the input resonator 22 and the triangular patch output resonator 24 is a magnetic coupling, so that the attenuation pole characteristic is formed at the lower side of the band. The conventional bandpass filter using the triangular patch resonator is suitable for a wireless communication system adapted to a high selectivity channeling and low insertion loss [J. S. Hong, M. J. Lancater (2000), “Microstrip triangular patch resonator filters”, IEEE MTTS digest, pp. 331-334].
FIG. 3 is a pattern diagram for illustrating a microstrip type bandpass filter according to a third example of the prior art, which is a pattern diagram of the resonator made of a multi-layer substrate.
Referring to FIG. 3, the microstrip type bandpass filter according to the third example of the prior art comprises an input terminal port1, an output terminal port2, input resonators L11, L12, and C1, upper resonators L21, L22, and C2, and output resonators L31, L32, and C3.
The three resonators formed in a typical multi-layer substrate comprise inductance portions and capacitance portions. The inductance portion of the second resonator couples that of the first resonator and that of the third resonator in the triangular form. In addition, the attenuation pole is formed below the passband by a cross coupling between the first resonator and the third resonator.
When a signal is input through the input terminal port1, the input signal resonates through the input resonator L11, L12, and C1, and the resonated signal is transferred to the upper resonator L21, L22, and C2 to resonate by the electric coupling, and again, transferred to the output resonator L31, L32, and C3 to resonate by the electric coupling. Next, the resonated signal is output through the output terminal port2.
Here, a main coupling of the filter is made of an electric coupling, and the coupling between the input resonator L11, L12, and C1 and the output resonator L31, L32, and C3 is a magnetic coupling. Therefore, the attenuation pole characteristic is formed at the upper side of the passband, and the attenuation pole characteristic and the frequency are adjusted by the cross coupling. The conventional bandpass filter uses an LC coupling resonator in the multi-layer substrate, which is suitable for a microwave device and miniaturization (U.S. Pat. No. 6,608,538 (Sep. 19, 2003)).
FIG. 4 is a pattern diagram for illustrating a microstrip type bandpass filter according to a fourth example of the prior art, which is a pattern diagram of a bandpass filter formed with an LC resonator, and the resonator type is an LC coupling resonator.
Referring to FIG. 4, the microstrip type bandpass filter according to the fourth example of the prior art includes three LC coupling resonators, a cross coupling gap, a cross coupling line or a mixed structure of a cross coupling gap and a cross coupling line on the substrate. Here, the microstrip type bandpass filter comprises an input terminal 30, an output terminal 31, an input resonator 32, an upper resonator 33, and an output resonator 34.
In addition, with regard to the coupling between the respective resonators, there exist a coupling 35 between the input resonator 32 and the upper resonator 33, a coupling 36 between the upper resonator 33 and the output resonator 34, a cross coupling gap 37 between the input resonator 32 and the output resonator 34, a cross coupling line 38 between the input resonator 32 and the output resonator 34, and the cross coupling gap 37 and the cross coupling line 38 between the input resonator 32 and the output resonator 34.
A microwave signal is flowed into the LC coupling input resonator 32 through the input terminal 30, transferred to the LC coupling upper resonator 33 through the electric coupling, and transferred again to the output terminal 31 via the LC coupling output resonator 34. In addition, the attenuation pole is formed at the upper and lower side of the passband by the cross coupling gap, the cross coupling line, or a combination thereof between the LC coupling input resonator 32 and the LC coupling output resonator 34.
The main coupling of the bandpass filter described above is an electric coupling, and the cross coupling is a magnetic coupling or an electric coupling, and it is suitable for a microwave device and miniaturization since the LC coupling resonator is used.
However, recently, the costs and the size of the passive device such as a bandpass filter should be significantly reduced due to a miniaturization of the millimeter wave system for the home network, telematics, the intelligent traffic system, and the satellite Internet. According to the prior arts, it is difficult to implement a bandpass filter having a minimum width of 2.0 mm or less. This is because, when the width is 2.0 mm or more, an unwanted waveguide mode is generated in a waveguide when shielding the bandpass filter.